Soil Mechanics

EXPERIMENT 4A Answers to Questions: 1. What is the purpose of the liquid limit test? The purpose of the liquid limit test is to determine the stress history and general properties of the soil met with construction; with the help of the liquid limit, the compression index can be estimated which would be helpful in the settlement analysis. 2. How do you define liquid limit? Liquid limit is the arbitrary limit of water content at which the soil is just about to pass from plastic state into the liquid state. At liquid limit, the soil possesses a small value of shear strength, losing its ability to flow as a liquid. The gist is that the liquid limit is the minimum moisture content at which the soil tends to flow as a liquid. 3. What is the main difference between wet specimen and dry specimen preparation methods for the liquid limit test? When conducting the wet specimen preparation method for liquid limit test, one must determine by visual or manual methods that the soil sample has little or no material retained on the # 40 sieve. If this is the case, prepare 150-200g of material by mixing thoroughly with distilled water. Adjusting the water content of the material would bring the soil to consistency which would require about 25-35 blows of the liquid limit device to close the groove made by the grooving tool. When conducting the dry specimen preparation method for liquid limit test, one must first dry the soil sample passing through the # 40 sieve at room temperature or in an oven dry not exceeding a temperature of 60deg C, until the soil clods pulverize readily. Pulverize the material using mortar and pestle or in some other way that does not cause a breakdown of individual particles. The procedure must be stopped once most of the fine material has been disaggregated and the material retained on the 425-µm sieve consists of individual particles. Adjusting the water content of the material would bring the soil to consistency which would require about 20-30 blows of the liquid limit device to close the groove made by the grooving tool. 4. Why do you use a special cup and cranking device to determine the liquid limit? Why not use another shape for the cup? A special cup and cranking device is used to determine the liquid limit because those are the standards of the ASTM and every test must comply with the ASTM standards (ASTM D4318). The cup can be adjusted for a 10mm fall and can be raised and dropped. Not only that but, the shape of the cup is curved in a way that the plasticity of moist soil can easily be seen.

5. Should you add or remove water to obtain a lower blow count? A lower blow count can be obtained by adding water to the paste. Additional amounts of water into the paste will help one obtain a lower blow count due to the paste being less sticky with respect to the cup. 6. What is the minimum number of data points required to determine the liquid limit? The minimum number of data points required to determine the liquid limit is two. Two individual points would draw a straight line. 7. What is the purpose of calibration of the Atterberg device? The purpose of the calibration of the Atterberg device is to attain consistency in the height of drop which, would be helpful in attaining accurate data. 8. Under what conditions would you use seawater to moisten a clay sample? Seawater is used to moisten a clay sample because it contains minerals that help penetrate into the clay sample. Distilled water cannot penetrate into a clay sample because clay has a compacted structure. 9. Is there a typical value for the liquid limit to clean fine sand? Justify your answer. No, there is no typical value for the liquid limit to clean fine sand because a confined mass of sand is not plastic. A confined mass of sand is elastic and has no Atterberg limits.

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